The present invention relates to a deciding apparatus for deciding an audio signal coding system and a deciding method using the same and, more particularly, a deciding apparatus for deciding an audio signal coding system using a DSP (Digital Signal Processor) and a deciding method using the same.
In recent years, the audio sources such as CD, LD, DVD, etc. have been spread and also PCM (Pulse Code Modulation), DTS, AC-3, MPEG, etc. have been practically used as the coding system for the audio signal recorded thereon. In order to decode the audio signals to which these coding systems are applied, the decoding methods that mate with the coding systems must be employed. Therefore, prior to the decoding of the audio signal, the coding system that has been applied to the audio signal must be decided.
The audio signal is input from the audio source (CD, LD, DVD, etc.) to the AV amplifier, the DVD player, the speaker system, etc. The audio signal from CD, LD, DVD is coded and the coding system is different for every audio source. The coding systems are shown in Table 1.
In Table 1, DTS is the coding system developed by Digital Theater Systems, Inc., AC-3 is the coding system developed by Dolby Research Institute, and MPEG (Moving Picture Experts Group) is the international standard of the information compressed coding system.
As can seen from Table 1, only a single coding system is not always applied to one audio source, but a plurality of coding systems may be applied to one audio source in some cases. In this case, the coding system may be changed in the middle of listening of one audio source. For example, there is such a case that, since DTS, AC-3, or MPEG can be applied to the DVD, first the audio source coded by DTS is listened and then switched to the same audio source coded by AC-3 or MPEG in the middle.
Therefore, in order to decode the audio signal, first it must be decided which coding system is applied to the audio signal at present. Then, the audio signal must be decoded according to the decoding method that corresponds to the decided coding system.
In the following, the deciding apparatus for deciding audio signal coding system employed in the prior art will be explained with reference to FIG. 1 hereunder.
FIG. 1 is a block diagram showing a deciding apparatus for deciding audio signal coding system in the prior art. In FIG. 1, 100 denotes a DIR (Digital Interface Receiver). The audio signal supplied from the audio source is converted into a predetermined signal format by the DIR 100, and then input into a DSP (Digital Signal Processor) 103.
The audio signal from the audio source is based on the digital audio interface standard called IEC958, and one frame of the audio signal consists of audio data and additional data. An information indicating that the audio signal is coded by either the PCM or a coding system (DTS, AC-3, or MPEG) other than the PCM is contained in the additional data.
If the audio signal is coded by the PCM, the DIR 100 turns ON a flag indicating this (referred to as a xe2x80x9cPCM flagxe2x80x9d hereinafter) based on this information, and then outputs the PCM flag to a microcomputer 101. Also, if the audio signal is coded by a coding system other than the PCM, the DIR 100 turns OFF the PCM flag, and then outputs the PCM flag to the microcomputer 101. Based on ON/OFF of the PCM flag, the microcomputer 101 can decide whether the present audio signal input is coded by a PCM or the coding system (DTS, AC-3, or MPEG) other than the PCM. However, if the audio signal is coded by a coding system other than the PCM, it cannot be decided only by the PCM flag which one of DTS, AC-3, and MPEG is used for the audio signal. A method of identifying DTS, AC-3, and MPEG in this case will be described later.
The DSP 103 decodes the audio signal input from the DIR 100. In order to decode the audio signal, the decode program which corresponds to the coding system applied to the audio signal must be previously loaded onto the DSP 103. The decode program necessary for the decoding is stored in a memory 102 in the microcomputer 101, and the program is loaded onto the DSP 103 according to the coding system applied to the audio signal.
Also, if the decode program which does not mate with the coding system applied to the audio signal is loaded onto the DSP 103, such DSP 103 has a function for outputting the decode error signal to the microcomputer 101. For example, since the coding system does not coincide with the decode program which is being loaded in case the coding system of the audio signal is changed in the middle of listening to the certain audio source, the DSP 103 outputs the decode error signal to the microcomputer 101. Accordingly, the microcomputer 101 can detect that the coding system of the audio signal has been changed.
Reference numeral 105 denotes an output mute device for muting the output from the DSP, and 104 denotes a D/A converter for converting the digital signal output from the DSP into the analog signal.
Next, a deciding method for deciding audio signal coding system using the deciding apparatus for deciding the audio signal coding system shown in FIG. 1 will be explained with reference to FIG.2.
FIG.2 is a flowchart showing a process for deciding audio signal coding system programmed in the microcomputer 101 in the prior art.
First of all, in step S101, according to the ON/OFF-switching of the PCM flag being output from the DIR 100 or the decode error signal, the microcomputer 101 detects that the coding system of the audio signal from the audio source has been changed.
Then, in step S102, the microcomputer 101 outputs the output mute signal to the output mute device 104 to mute the output.
In turn, in step S103, the microcomputer 101 outputs the decode program halt instruction to the DSP 103 to halt the current decode process being executed in the DSP 103.
Then, in step S104, it is decided whether or not the coding system of the audio signal supplied from the audio source is either the PCM system or another system (DTS, AC-3, or MPEG). This decision is made based on ON/OFF of the PCM flag from the DIR 100. In other words, the microcomputer 101 decides that the coding system is the PCM system if the PCM flag is ON, while it decides that the coding system is another system (DTS, AC3, or MPEG) if the PCM flag is OFF.
At this time, in step S104, if it is decided that the coding system of the audio signal from the audio source is the PCM system (if YES), the process goes to step S105. Then, the PCM decode program stored in the memory 102 is loaded onto the DSP 103. Then, the process goes to step S106, and the decode process start signal is output to the DSP 103 and the decode process is restarted in the DSP 103. After this, the process advances to step S107, and then the microcomputer 101 outputs the output mute release signal to the output mute device 104 to release the output mute, whereby the process for deciding audio signal coding system is ended.
In contrast, in step S104, if it is decided that the coding system of the audio signal from the audio source is not the PCM system (if NO), the process goes from step S104 to step S108. Then, in step S108, the DTS decode program is loaded from the memory 102 onto DSP 103. Then, the process advances to step S109, where the microcomputer 101 outputs the decode process start signal to the DSP 103 to cause the DSP 103 to restart the decode process. Then, the process goes to step S110, where the microcomputer 101 decides whether or not the decode error signal supplied from the DSP 103 is present. Such decode error signal is output from the DSP 103 to the microcomputer 101 when the coding system applied to the audio signal currently does not coincide with the decode program loaded onto the DSP 103. For this reason, in step S110, if there is no decode error signal (if NO), it can be understood that the coding system applied currently to the audio signal is DTS. In this case, there is no need to load another decode program (for AC-3 or MPEG) onto the DSP 103, and thus the process goes to step S107. The output mute is released in step S107 and then the decision process of the coding system is ended.
In contrast, in step S110, if there is the decode error signal (if YES), the process is proceeded from step S110 to step S111. In step S111, the AC-3 decode program is loaded from the memory 102 onto DSP 103. Then, the process goes to step S112, and then the microcomputer 101 outputs the decode process start signal to the DSP 103 to restart the decode process in the DSP 103. Then, the process goes to step S113, and then the microcomputer 101 decides whether or not the decode error signal supplied from the DSP 103 is present. At this time, in step S113, if there is no decode error signal (if NO), it can be understood that the coding system applied currently to the audio signal is AC-3. In this case, there is no need to load another decode program (for MPEG) onto the DSP 103, and thus the process goes to step S107. The output mute is released in step S107 and then the decision process of the coding system is ended.
In step S113, if there is the decode error signal (if YES), the process is shifted from step S113 to step S114. In step S114, the MPEG decode program is loaded from the memory 102 onto DSP 103. Then, the process goes to step S115, where the microcomputer 101 outputs the decode process start signal to the DSP 103 to restart the decode process in the DSP 103. At this time, since the coding systems (PCM, DTS, or AC-3) other than the MPEG have already been decided in step S104, S110, S113, there is no coding system except the MPEG as the coding system which is applied currently to the audio signal. Accordingly, since there is no necessity to decide whether or not the decode error signal is present after step S115, the process goes to step S107. Then, the output mute is released in step S107 and then the process for deciding audio signal coding system is ended.
According to the above deciding apparatus for deciding audio signal coding system and the deciding method using the same in the prior art, it is decided based on the PCM flag from the DIR 100 whether or not the coding system is either the PCM or remaining systems (DTS, AC-3, or MPEG), then the decode program for the system (DTS, AC-3, or MPEG) other than the PCM is loaded from the memory 102 to the DSP 103 if it is decided that the coding system corresponds to the system other than the PCM, and then the coding system is decided based on whether or not the decode error signal supplied from the DSP 103 is present.
However, the above deciding apparatus for deciding audio signal coding system and the deciding method using the same have the following problems.
That is, when the coding system (DTS, AC-3, or MPEG) other than the PCM is applied to the audio signal, the PCM flag supplied from the DIR 100 does not provide to the microcomputer 101 information indicating which coding system of DTS, AC-3, or MPEG is employed. In order to identify DTS, AC-3, or MPEG, the microcomputer 101 must load the decode programs corresponding to these coding systems from the memory 102 to the DSP 103 several times.
Since the communication rate between the microcomputer 101 and the DSP 103 is about 200 kbps at the utmost, it takes too much time to load the large decode program onto the DSP 103 at this communication rate. In the case where the longest time is required, it takes about 500 msec to load one decode program. Thus, if the process goes up to step S114 in FIG.2 (i.e., the decode programs of DTS, AC-3, or MPEG are loaded sequentially), a time of about 1.5 sec (=3xc3x97500 msec) is required.
The microcomputer 101 must execute processes such as the display, the remote control, panel control, etc. in addition to the decision of the audio signal coding system. Because these jobs are temporarily held during the decision process of the coding system, the decision process of the coding system interferes with these jobs if too much time is required for such decision process of the coding system.
It is an object of the present invention to provide a deciding apparatus for deciding audio signal coding system capable of deciding the coding system of the audio signal in a shorter time than the prior art, and a deciding method for deciding audio signal coding system using the same system.
According to the deciding apparatus for deciding audio signal coding system described in the present invention, the apparatus comprises a DSP (Digital Signal Processor) for deciding audio signal coding system and decoding the audio signal, a storing means for storing decode programs necessary for the decoding of the audio signal by the DSP, and an output muting means for muting the output from the DSP. It is the DSP that executes the decision of the coding system of the audio signal, and thus the microcomputer is not employed to decide the coding system, unlike in the prior art.
Therefore, the DSP is not requested to communicate with the microcomputer. As a result, the time necessary for such communication is eliminated and thus the time consumed to decide the coding system is reduced.
Also, according to the deciding method for deciding audio signal coding system described in the present invention, the coding system is decided based on the data sequence in the predetermined portion of the additional data in the audio signal.
Therefore, the time consumed to decide the coding system is reduced compared with the conventional deciding method in which the decode program must be loaded into the DSP several times.